Method for improving the magnetic properties of ferrous alloys



Feb. 27, 1940. DAHL AL 2,192,032 METHOD FOR IMPROVING THE MAGNETICPROPERTIES OF FERROUS ALLOYS Original Filed Feb. 15, 1956 2 Sheets-Sheet1 Fig. l.

0 I Inventors: Otto Dahl, Franz Pawle by 6) 4 Then Att orne y.

Feb. 27, 1940. O. DAHL El AL. 2,192,032 METHOD FOR IMPRQVING THEMAGNETIC PROPERTIES OF FERROUS ALLOYS Original Filed Feb. 15, 1936 2Sheets-Sheet 2 Inventors: Otto Dahl, Franz Pawlek y Their Attorney.

Patented Feb. 27,

METHOD FOR IMPROVING THE MAGNETIC PROPERTIES OF FERROUS ALLOYS OttoDahl, Berlin-Friedman, and Franz Pawlek, Bcrlin-Niederschoneweide,Germany, assignors to General Electric Company, a corporation of NewYork Original application February 15, 1936, Serial No.

s PATENT OFFICE 64,138. 26, 1938, Serial March 11, 1935 Divided and thisapplication October No. 237,156. In Germany 3 Claims. (01. 148-4) Thisapplication is a division of our copending application, Serial No.64,138, filed February 15, 1936, now Patent 2,145,712, January 31, 1939,and entitled Method for improving the magnetic properties of ferrousalloys.

In order to obtain a uniform rise of magnetization throughout a widefield-strength range, as

well as a nearly complete saturation at low field strengths, it has beenproposed to produce in magnetic materials, an ordered grain texture suchas can be obtained by certain rolling and annealing processes. Forinstance, magnetic iron-nickel alloys can be cold-rolled, prior to thefinal annealing, with a reduction of thickness amounting to more than90%, preferably more.

than 95%, after which the material is annealed at temperatures above therecrystallization limit. As a result of this treatment, an orderedposition of the crystallites is obtained in the plates after theannealing, and this ordered position has an extraordinary favorableinfluence on the magnetic properties. 1

The present invention is an improvement of these methods and consists insubjecting the alloys during cooling, after the final annealing, to theinfluence of a magnetic field, in such a way that, depending uponwhether the magnetization curves, as a function of the field strength,are to have a steeper or fiattershape, the-alloys are subjected eitherto the influence of a longiudinal' or transverse magnetic field. Theterms, longitudinal and transverse, here, imply respectively thedirection of rolling or the direction at right angles to the directionof rolling. While the influence of a magnetic field applied during menswhich, for thepurpose, of an ordered grain structure, have beensubjected, prior to the final annealing, to a cold rolling resulting ina decrease in thickness exceeding 90%. On the other harid. the curvesdenoted by b represent the results obtained with specimens that had beensubjected to a lesser amount of cold rolling such as had been resortedto formerly. The indexes l to 3 indicate whether the alloy specimenswere subjected to a magnetic field during the cooling and, if so, towhat magnetic field. Specimens with index I were cooled without theapplication of a magnetic field; the specimens with index 2 were cooledwith the simultaneous application of a longitudinal magnetic field,while specimens with index 3 were cooled with the simultaneousapplication of a transverse magnetic field.

Fig. 1 refers to a binary iron-nickel alloy with 40% nickel and iron;Fig. 2 refers to a binary iron-nickel alloy having equal parts of ironand nickel, while Fig. 3 refers to an iron-nickelcobalt alloy with 45%nickel, 30% iron and 25% cobalt. The alloy specimens were producedtogether and in exactly the same manner. All were obtained from acasting produced in a high frequency furnace from technically purematerials;

they were then reduced to a thickness of 0.3 mm. by way of florging orhot or cold rolling with intermediate annealing above therecrystallization temperature. The specimens of group b were subjected,during the last cold rolling to a decrease in thickness amounting tothat is, a decrease in thickness which is close to the limit of theconventional rolling process used in connection with such alloys. Incontrast to this, the specimens of group a were, in order to attain agood grain structure, subjected to a last cold wider induction range. Onthe other hand, the

simultaneous application of a high degree of cold I rolling and of atransverse magnetic field during cooling, results always in amagnetizing curve which is rectilinear through an unusually widefield-strength range. In particular,-the magnetization characteristic ofthe alloy represented in Fig. 2, which consists of equal parts of ironand nickel, is steeper than that of the magnetization curve of the alloyaccording to Fig. 1, which alloy has 40% of nickel and 60% of iron.Thus, if for certain reasons, a linear magnetization characteristic isdesired through a field-strength range which is as wide as possible. thealloy. ac-

cording to Fig. 1, should be given preference to the alloy according toFig. 2. This condition will always obtain whenever the field strengthcannot be reduced at will by the selection of a small number of turns ina coil. However, if this reduction is possible, so that whendimensioning a coil, only the induction need be considered, the alloy,according to Fig. 2, should be given preference over the alloy of Fig.1, for with the alloy, according to Fig. 2, the same eiTect can beobtained with a smaller amount of material.

Fig. 3 shows that the application of the method, according to theinvention, is not limited to binary iron-nickel alloys, but that it canbe also successfully applied to the iron-nickel-cobalt alloys. Theimprovement of the steep rise of the characteristic by the simultaneousapplication of a high degree of cold rolling and a longitudinal'magnetic field during the cooling is, here, not so marked as was thecase with the application of the longitudinal magnetic field inconnection with the binary iron-nickel alloys, for the application of amagnetic field alone, permits obtaining a very steep curve. On the otherhand, the improvement of the linear rise through a wide field-strengthrange, by applying simultaneously a high degree of stretching and atransversal magnetic field, is here quite considerable; Fig. 3 showsthat the uniform rise begins practically at the point of origin and thatit continues until saturation sets in. The hysteresis loop returns withthe low remanence of a thousand gauss, nearly as linearly as it rises.Such an alloy is of major importance for communication engineering, forinstance for Krarup lines, and also for transmitters, for a magneticbody consisting of that particular alloy, operates practically withoutharmonics. For this reason, an alloy oi' that composition and treatmentmust be primarily applied in all those cases which deal with circuits inwhich the harmonics have a disturbing eflfect, even at a slightamplitude. Such fields of application exist always in those casesmitting range .of the other channel and maythilissentail a mutualinterference of both channe 4 The application or the object or theinvention is not limited to the alloys which have been chosen by way ofexample. The entirely diiierent composition of the alloys in Figs. 1 and2 on the one hand, and in Fig. 3 onthe other hand, indicates plainlythat the method according to the invention will permit a considerableinfluencing of the magnetic properties in nearly all ferromagneticsubstances. Which one of the known alloys must be chosen for anyparticular purpose, can be determined from case to case by a simpletest. The method is particularly advantageous in connection with allthose alloys in which the application of the conventional an- What weclaim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A method for improving the magnetic properties of alloys consistingof nickel and iron which comprises cold working the alloy to effect areduction in thickness of more than 90%, annealing the alloy and duringcooling subjecting it to the influence of a transverse magnetic field.

2. A method for improving the magnetic properties of alloys consistingof iron and metal from the group nickel and cobalt which comprises coldworking the alloy to efiect a reduction in thickness of more than 90%,annealing said alloy and during cooling" subjecting it to the influenceof a transverse magnetic field.

3. A method for improving the magnetic properties of alloys consistingof iron and metal from the group nickel and cobalt which comprises coldrolling the alloy toefiect a reduction in thickness of more than 90%,annealing the rolled metal and during cooling subjecting it Y to theinfluence of a magnetic field which is applied in a direction transverseto the direction in which the metal was cold rolled.

OTTO DAI IL. FRANZ PAWLEK.

